P. Wagner

Directed flow in Au+Au, Xe+CsI, and Ni+Ni collisions and the nuclear equation of state

We present new experimental data on directed flow in collisions of Au+Au, Xe+CsI and Ni+Ni at incident energies from 90 to 400A MeV. We study the centrality and system dependence of integral and differential directed flow for particles selected according to charge. All the features of the experimental data are compared with Isospin Quantum Molecular Dynamics (IQMD) model calculations in an attempt to extract information about the nuclear matter equation of state (EoS). We show that the combination of rapidity and transverse momentum analysis of directed flow allow to disentangle various parametrizations in the model. At 400A MeV, a soft EoS with momentum dependent interactions is best suited to explain the experimental data in Au+Au and Xe+CsI, but in case of Ni+Ni the model underpredicts flow for any EoS. At 90A MeV incident beam energy, none of the IQMD parametrizations studied here is able to consistently explain the experimental data.

Study of the 40Ar + 68Zn reaction at 27.6 MeVNucleon

Abstract The various reaction mechanisms observed in the 40 Ar(1102 MeV) + 68 Zn reaction have been studied. Projectile-like fragments appear to result, in addition to deep-inelastic collisions, from projectile breakup, i.e. a process bearing a close similarity to high-energy fragmentation, and from direct transfer of nucleons. The origin of light fragments (4 ≲ Z ≲ 10) can be explained in terms of three distinct sources; one moving with the projectile velocity, a second having a velocity corresponding to full transfer of the projectile linear momentum to the projectile-plus-target system, and a third source moving with a velocity intermediate between the first two and corresponding to a very excited and non-equilibrated localized region of the nuclear system. The heavy fragments result essentially from an incomplete fusion process. Some features of the various types of fragments have been calculated. Comparisons with existing models are presented.

Differential directed flow in Au + Au collisions

We present experimental data on directed flow in semi-central Au+Au collisions at incident energies from 90 to 400 A MeV. For the first time for this energy domain, the data are presented in a transverse momentum differential way. We study the first order Fourier coefficient v1 for different particle species and establish a gradual change of its patterns as a function of incident energy and for different regions in rapidity.

Azimuthal anisotropies as stringent test for nuclear transport models

Abstract Azimuthal distributions of charged particles and intermediate mass fragments emitted in Au+Au collisions at 600 A MeV have been measured using the FOPI facility at GSI-Darmstadt. Data show a strong increase of the in-plane azimuthal anisotropy ratio with the charge of the detected fragment. Intermediate mass fragments are found to exhibit a strong momentum-space alignment with respect of the reaction plane. The experimental results are presented as a function of the polar centre-of-mass angle and over a broad range of impact parameters. They are compared to the predictions of the Isospin Quantum Molecular Dynamics model using three different parametrisations of the equation of state. We show that such highly accurate data provide stringent test for microscopic transport models and can potentially constrain separately the stiffness of the nuclear equation of state and the momentum dependence of the nuclear interaction.

Isospin dependence of relative yields of

Results on

K^+

K^+

and

and

K^0

K^0

mesons at 1.528 A GeV

meson production in

Charged pion production in 44 96Ru + 44 96Ru collisions at 400A and 1528A MeV

^{96}_{44}